This invention relates generally to controlling tension in a recording medium.
Recording media for imaging systems is stored in rolls in a media cassette or other type of storage area. Uneven tension in the recording media as it is fed from these rolls can cause problems, such as velocity disturbances and undesired directional steering. Velocity disturbances can cause imaging artifacts and dimensional inaccuracies in the resulting images. Directional steering, if subtle, can cause dimensional inaccuracies in the resulting images and, if severe, can result in recording media jams.
In general, in one aspect, the invention is directed to controlling tension in a medium fed from a roll. This aspect of the invention features detecting a rotational velocity of the roll as the medium is fed and applying a torque to the roll to maintain tension in the medium. The torque is applied by a motor that is controlled based on the rotational velocity of the roll. The invention may also include one or more of the following features.
A controller controls the torque applied by the motor by controlling an amount of current supplied to the motor. A switchable media cassette stores the roll of recording media. The motor is capable of applying sufficient torque to rewind the medium onto the roll. An encoder, such as a digital tachometer, measures the rotational velocity of the roll. The controller is a motor servo. A coupling is controlled by the motor to apply the torque to the roll. The coupling includes one or more pulleys.